AJP - Cell Physiology, Vol 236, Issue 5 185-C191, Copyright © 1979 by American Physiological Society
Isometric endurance in fast and slow muscles in the cat
J. S. Petrofsky and A. R. Lind
By use of a method of sequential stimulation described previously, the
ability to sustain tensions of 3--100% of the initial strength (maximum
isometric tension that could be developed in the fresh muscle) to fatigue
(endurance) was assessed in the soleus (slow-twitch), medial gastrocnemius
(mixed, fast-twitch), and plantaris (mainly fast-twitch) muscles. For all
fractions of the initial strength the endurance was longest in soleus and
shortest in plantaris. However, although plantaris fatigued at any tension
examined, soleus could maintain a tension of up to 30% of its initial
strength indefinitely with no sign of fatigue. Part of the difference in
endurance between these two muscles could be accounted for in terms of
blood flow because arterial occlusion sharply reduced the endurance of
soleus but had only a small effect on endurance in plantaris. However, even
with an occluded circulation, soleus still had substantially longer
endurance than either medial gastrocnemius or plantaris. The origin of
fatigue in any of the three muscles examined appeared to be in the muscle;
there was no evidence of failure of transmission at the neuromuscular
junction.
